The invention is generally concerned with fluid pumps or motors of the rotary axial piston type, and in particular with an improved variable displacement device of this type. For the purposes of convenience, the invention will be described as a fluid pump, but it should be understood that the term pump when used hereafter in the specification and claims embraces both a fluid pump and a fluid motor.
Such devices comprise a casing within which is a rotary cylinder barrel having a plurality of parallel cylinder bores within which pistons reciprocate, the pistons extending from the cylinder barrel to either directly abut camming means, such as a thrust plate member, or being associated therewith by means of articulated connecting rods. The cylinder barrel rotates against a valve plate having inlet and outlet ports, which serves in a well-known manner to provide properly phased communication between the end ports of the cylinder bores within which the pistons reciprocate and inlet and outlet passages of the device. Examples of the type of devices described are disclosed in U.S. Pat. No. 3,108,542.
In such devices, the axis of the thrust plate member is inclined relative to the axis of rotation of the cylinder barrel for reciprocating the pistons, the total displacement of the device being resolved by the relative angle of inclination between the axes of the two members, since the displacement of each piston is determined by the area of the cylinder bore and the length of stroke of the piston, and the length of stroke of the piston is determined by the relative angle of inclination of the axis of rotation of the cylinder barrel and the axis of the thrust plate member.
It has been the practice, therefore, to vary the displacement of such devices by providing a swinging yoke for changing the angle of tilt of the cylinder barrel to vary piston stroke length or by providing mechanism for changing the angle of tilt of the thrust plate member to vary piston stroke length, which yoke or other mechanism may be manually or fluid pressure operated. Examples of two such forms of variable displacement devices are disclosed in U.S. Pat. Nos. 2,565,208 and 2,708,879.
It has also been proposed and has been used successfully to provide a fluid pressure energy translating device of the rotary axial piston type which includes a housing, a rotary cylinder barrel and associated pistons, a cam block and a rotatably mounted valve plate which can be rotated to vary the displacement of the pumping mechanism as shown in U.S. Pat. No. 3,108,542.
Among the objectives of the present invention are to provide a variable delivery energy translating device of an improved type which does not require the use of a movable yoke plate or the use of a rotary valve plate.
In accordance with the invention, a fluid pressure translating device comprising a housing with a pumping mechanism therein including a rotary cylinder barrel having a plurality of cylinders with pistons slidable therein operatively associated with a cam block, each cylinder having a port opening to a valving base of the cylinder barrel and means forming an inlet and outlet passage and a valve plate associated with the cylinder barrel and provided with inlet and outlet ports respectively in communication with the inlet and outlet passages. The cam block is rotatable to vary the circumferential position of the cam block relative to the valve plate thereby varying the displacement pumping mechanism.